Coral insects inhabiting sea areas in the temperate zone, the subtropical zone and the tropical zone form coral reefs. The coral reefs weather and one after another turn into spalls or particles with lapse of thousands to tens of thousands of years after the death of coral insects living in the coral reefs. Such spalls or particles are carried by ocean currents, and they settle on the sea bed according to particle size by the action of the levigation in ocean currents and accumulate there. The weathered reef-building coral is an accumulation of such spalls or particles.
The weathered reef-building coral have a very porous fine structure. This porous fine structure is a dwelling site of the inhabitation of coral insects, and organic substances originating from various marine algae and microorganisms (e.g., Vibrio bacteria) inhabiting the ocean are held therein while the weathered reef-building coral exists at the sea bed for many years.
The weathered reef-building coral is utilized as food materials for supplementing calcium, or as filter mediums for water purifiers, agricultural soil conditioners and so forth. When it is used in food materials and filter mediums for water purifiers, it is required to remove the above organic substances from the viewpoint of safety, and is also required to take measures for disinfection or sterilization so that microbiological safety can be ensured.
As a conventional process by which weathered reef-building coral materials used as food materials are manufactured from the weathered reef-building coral, the following steps are taken, as schematically shown in FIG. 4.
That is, first, the weathered reef-building coral is collected from the sea bed by a pumping boat, and is classified according to manufacture purposes into portions with predetermined particle or grain size [e.g., passing a 10-mesh sieve (particle diameters of 2.0 mm or smaller) and leaving on a 80-mesh sieve (particle diameters of 0.18 mm or larger)]. The weathered reef-building coral thus classified is landed and thereafter stored in a stockyard, and the greater part of sea water salt is removed therefrom by spraying city water over the whole, followed by air-drying. This is then brought into a factory, and is sieved in the factory yard by a vibrating sifter according to the predetermined particle or grain size, which is again washed with water using a washing machine, followed by dehydration and drying and further followed by dry heat disinfection or dry sterilization usually at 100 to 200.degree. C. The resultant material is pulverized and sifted to adjust their particle or grain size to a predetermined particle or grain size, and then packaged for commercialization. Alternatively, the material brought into a factory, sieved, and washed with water followed by dehydration and drying is then roasted at a temperature within the rage where calcium carbonate, the main component of the weathered reef-building coral, is not decomposed (250 to 600.degree. C.), and this is pulverized and sifted to adjust their particle or grain size to a predetermined particle or grain size and then packaged for commercialization. The weathered reef-building coral material for food thus obtained is made to have particle diameters small enough to pass a 300-mesh sieve, i.e. particle diameters of 45 .mu.m or smaller.
As a conventional process for manufacturing filter mediums for water purifiers, like the above process for manufacturing weathered reef-building coral materials for food, the weathered reef-building coral is collected, sieved in the factory yard by a vibrating sifter to sift grains to have a predetermined size to thereby uniform their grain size to a size suitable for the filter mediums for water purifiers, followed by washing with water, dehydration and drying. Subsequently, the resultant weathered reef-building coral is roasted (250 to 600.degree. C.) so as to be activated to enhance mineral elution quantity, which is then sifted to adjust the grain size to a predetermined size, and packaged for commercialization.
Silver-added materials prepared by coating the weathered reef-building coral with silver are known to be improved in sterilizing ability (Japanese Patent Application Laid-open No. 51-179107, etc.). As the silver-added materials, those having grain diameters of 0.71 mm or larger which are used chiefly as filter mediums for water purifiers and those having grain diameters smaller than 0.71 mm which are used for other purposes are manufactured. As a process for manufacturing such silver-added materials, the filter mediums for water purifiers described above, the weathered reef-building coral is roasted in the same manner as in the case of the filter mediums for water purifiers described above. Thereafter, it is immersed in an aqueous silver solution, immersed in a reducing agent solution such as an ascorbic acid solution, and heated at 400.degree. C. for about 30 minutes to cause silver to deposit, followed by washing with water, drying and packaging for commercialization.
However, in the conventional process for manufacturing weathered reef-building coral materials for food or filter mediums, various marine algae having grown for many years, various microorganisms including Vibrio bacteria inhabiting the ocean and other organic substances can not be removed from the inside of the porous fine structure of the weathered reef-building coral. Hence, the conventional process is insufficient in view of the ensuring of safety required for food materials.
In general, as well known, in water purifiers in which the weathered reef-building coral having been subjected to the step of heating by dry heat disinfection or dry sterilization, or by roasting is set as a filter medium, minerals flow out in a small quantity when water is run, so that the taste of water can be improved. However, the weathered reef-building coral materials obtained by the conventional process can not elute minerals so much as to greatly enhance total hardness elution quantity. Also, it has not a sufficient degree of activation and hence can not be said to have a good adsorptivity for impurities or the like.
In the case when the silver-added weathered reef-building coral material is manufactured, there is also the problem that the silver is coated only on the surface of the weathered reef-building coral and is not coated throughout the porous inner fine structure.
The present invention solves the above problems the prior art has had. Accordingly, an object thereof is to provide a weathered reef-building coral material from which various marine algae, various microorganisms including Vibrio bacteria inhabiting the ocean and other various organic substances held in the inner fine structure of weathered reef-building coral have been removed and thereby its safety required as food materials has been ensured, and also to provide a process for manufacturing such a weathered reef-building coral material.
Another object is to provide food materials and filter mediums comprised of such a weathered reef-building coral material.
Still another object is to provide a silver-added weathered reef-building coral material coated with silver on its surface and also throughout its fine structure inside the porous tissue, and also to provide a process for manufacturing such a weathered reef-building coral material.
A further object is to provide an apparatus useful for manufacturing such a weathered reef-building coral material.